Cloud computing is a technique in which a user uses IT resources prepared in a data center as a service. The cloud computing is classified into SaaS (Software as a Service), PaaS (Platform as a Service), and IaaS (Infrastructure as a Service), according to a service form of the IT resources. The SaaS is to provide application software as a service, and the PaaS is to provide development environment or execution environment of the application software as a service. In addition, the IaaS operates a virtual machine on request of a user, on a physical machine connected to a network system of a data center, so as to provide resources of the virtual machine as a service.
By the cloud computing technique, the user of the IT resources can obtain advantages that reduction of initial investment can be expected and the used IT resources can be easily increased or decreased according to a necessary amount. On the other hand, in the cloud computing technique, a plurality of users share the IT resources of the data center, and thus it is pointed out that response to non-functional requirement such as performance is weak. In the IaaS, when the virtual machine is newly operated on request of the user, it is important to consider which physical machine should be operated for efficiently operating the virtual machine on the whole system, from a plurality of physical machines connected to the network system of the data center, from the view point of the response to the non-functional requirement. That is, by the selection of the physical machine operating the new virtual machine, a problem may occur, in which load of a network concentrates on a specific portion, or the virtual machines which need to communicate with each other are disposed to perform communication through a network path with a long delay, so that performance necessary in the whole network system is not satisfied. For this reason, it is desirable to provide a technique of determining a physical machine optimal to operate the new virtual machine, so as to efficiently dispose the virtual machine on the whole system.